Genetics: Sexual Reproduction and Meiosis

Sexual reproduction involves the fusion of male and female gametes, resulting in offspring that genetically differ from each other and their parents.
Gametes are produced through a process of cell division known as meiosis.
Meiosis involves two divisions of the nucleus and results in four non-identical daughter cells, each containing half the number of chromosomes as the parent cell.
The term haploid is used to describe cells (like gametes) that have half the number of chromosomes.
In contrast, body cells are diploid as they contain the full set of chromosomes.
The first stage of meiosis is the replication of the genetic material. Each chromosome makes an exact copy of itself.
These copies pair up and ‘crossing over’ occurs where equivalent sections of DNA are exchanged between chromosomes. This leads to genetic variation.
Independent assortment also contributes to genetic variation as it dictates which chromosome from each pair will make it into the gamete.
At fertilisation, the male and female gametes combine to form a zygote with the full complement of chromosomes.
The combination of genes in the offspring (from both parents) leads to variation in traits, some of which may be advantageous for survival and reproduction. This is the mechanism of natural selection.
Genetic disorders can occur due to abnormalities, mutations or changes in either single genes, group of genes or chromosomes.
Knowledge of genetics allows us to predict the possibility of an individual inheriting certain genetic conditions. This is done through punnett squares and genetic pedigree diagrams. It is important in fields like genetic engineering and gene therapy.
Scientists can also manipulate genetic processes to achieve certain outcomes, such as producing genetically modified organisms (GMOs). These manipulations can have both positive and negative impacts and raise important ethical considerations.